"Teachers retain a professional responsibility to their students, particularly those who are deemed vulnerable because of their age."
All names and identifying details have been suppressed to protect the former student.
The teacher told the tribunal's complaints assessment committee in May 2015, before they married, that there had been "no sexual relationship".
"She repeated those denials in a meeting with the [committee] in December 2015 and said she had not really had any contact with the student during the past four years," the tribunal said.
"However she was living with him at the time and married him the following month."
The tribunal did not accept her claim that the relationship only started in July 2015.
"We, however, found Teacher C to be neither a truthful nor reliable witness and reject her evidence that this is when the relationship began," it said.
Instead, it found that the couple began an intimate relationship in early 2013 when the former student was in jail.
"The student was vulnerable, and at the time the intimate relationship commenced Student A would have been in his last year of school or just finished it, had he not been in prison," the tribunal said.
It found that the age difference between them was relevant as it "tends to accentuate the power imbalance".
The tribunal found that the teacher was guilty of "serious misconduct". She was censured and her teaching registration was cancelled.
